Hello,

I'm thinking about the construction of my first router. A gantry type, about 6x3x1. As versatile as possible regarding usage.
I live in Argentina, here is very difficult to obtain and import equipment so I must choose very well.

I'm considering Mach3 and I have some questions.

As I understand Mach3 works as a trajectory generator, open loop. So Mach3 does not care about the motor-drive combo as long as they accept pulse & dir. It could be open loop steppers, closed loop steppers or servos. Is that correct?

If the above is correct I'd like to use servos (closing the loop only in the drive, no motion controller), and I see some AC servo & drive economic options. I am considering the following alternatives, and would like some feedback on them and other options in the same price range.

At the moment my preferences are:

AC servo & drive
http://www.americanmotiontech.com/Products/BrushlessServos/Sets/default.aspx?type=1
http://www.cnc4pc.com/Store/osc/index.php?cPath=97_99

closed loop stepper
http://www.americanmotiontech.com/Products/HybridServos/Sets/

open loop steppers
gecko

I am new in this area and any advice is welcome.
Thanks and regards,

Martin

I'm also very interested in this topic.
I'm hoping to use linear encoders.

I understand that backlash will throw a monkey wrench into the system, but let's say for the sake of argument that there is no backlash in the system.

If I set Mach3 to move 1000 steps per mm and I enter G-code to move an axis 1mm at a certain feed rate.
The servo driver will get 1000 step commands at the set feed rate, correct?
Will the servo driver verify through linear encoders that it has move the 1mm specified by 1000 steps?

Hoping I can either verify this before dropping coin on upgrades.

Thanks for any input.

Has anybody got more info on this? Im looking to build a mill with servos rather than non encoded steppers, and want to make sure its worth the effort.

What is your question?

The above mentioned servos will work fine with Mach3.
I plan on using the 400watt Leadshine servos from AMT in the first link for the new router I'm building, but I haven't purchased them yet.

You can and have always been able to use servos with Mach when using the parallel port.
There are a few things to bear in mind however, first is that your drives have to accept Step/Dir signals and second is your steps per unit are constrained by the kernel speed of the parallel port and thus you will either have to use lowish count encoders or your drives will have to be capable of electronic gearing.
With servos that use Step/Dir commands the loop is closed in the servo drive and feedback is to the drive.
Feedback usually takes the form of the motors encoder but you could also use linear encoders although any backlash at all would make this very difficult to tune if you did use linear encoders rather than the motors. Some servo drives can accept dual feedback but they are not common and certainly not in the lower end of the scale.

I have servos on all my machines but I use external controllers on all. Originally I used the parallel port on the big lathe but that was because there was no viable controller at the time. When using the parallel port I had to use the electronic gearing in my servo drives as realistically 45 to 65KHz is the most you are likely to get reliably from the parallel port.
 I am now moving over to external controllers that can control analogue command servo drives as you not only have closed loop in the external controller but you also have update of DRO position in Mach from the encoder information.

Hood

Those leadshine items look like a fairly reasonably priced solution. So, the combos that come with the motors, and drives would be a good match for mach3 control? With separate outboard servo drives, is here still need for a control box with break out board,, or just a hub for power supply?

Motors and drives need to be a good match for your machine, not Mach3. Anything that takes step/dir will work with Mach3.

How you wire it and what components you need is entirely up to you.

Well, Im trying to match servo motors output shaft size to the readily available ball screw size. This is determined by what is included in the cnc retrofit kit(s). Some are 8mm, and some are 1/4"  Of course, a nema23 size frame in the mid range power and wattage wize is about right for a small mill(bf20). So, making everything match up physically, and electronically is actually a bit complicated. My router works great on stepper motors, but it seems like servos are the way to go when making heavy hogging cuts. The router loses steps if pushed too hard. When I mention heavy hogging,, I mean in terms of a 300 pound bench mill,, so I know, not real heavy,, but presumably much deeper than the aluminum framed router can handle.

You can get couplers that connect shafts with different diameters.

The 200W Leadshines have an 11mm shaft I think.
The 400w has a 14mm shaft.

Well, Im trying to match servo motors output shaft size to the readily available ball screw size. This is determined by what is included in the cnc retrofit kit(s). Some are 8mm, and some are 1/4"  Of course, a nema23 size frame in the mid range power and wattage wize is about right for a small mill(bf20). So, making everything match up physically, and electronically is actually a bit complicated. My router works great on stepper motors, but it seems like servos are the way to go when making heavy hogging cuts. The router loses steps if pushed too hard. When I mention heavy hogging,, I mean in terms of a 300 pound bench mill,, so I know, not real heavy,, but presumably much deeper than the aluminum framed router can handle.

Servos are NOT inherently any better than steppers at anything.  For machines in the size range you're talking about steppers are perfectly capable of performing every bit as well as servos under any conditions the machine itself can handle IF the stepper system is properly designed.  Of course, a badly designed servo system is also quite capable of performing very badly.  My "big" machine, a Novakon Torus Pro runs steppers, and is capable of 350 IPM rapids, and taking "hogging" cuts a BF 20 could not even dream of.  Servos add absolutely nothing to the real-world performance, other than slightly less noise.

Regards,
Ray L.